Earlier studies showed that IA-2 and IA-2beta are enzymatically inactive members of the protein tyrosine phosphatase family, widely distributed in neuroendocrine cells throughout the body and transmembrane components of DCV. Further studies showed that IA-2/IA-2beta belong to an ancient gene family going back 500 million years with homologs in Drosophila and C. elegans Studies over the last year, in mice, showed that IA-2/IA-2beta which influences the secretion of hormones also modulates the secretion of neurotransmitters in the brain. These observations led to the discovery that the knockout of the IA-2/IA-2beta genes resulted in profound changes in behavior, learning and lifespan. Additional studies revealed that the knockout of IA-2/IA-2beta also had a profound effect on the circadian rhythm of blood pressure;heart rate, body temperature and physical activity. These observations point to the possibility that in mice and in humans, alterations in one or more of the many non-circadian structural proteins of secretory vesicles may similarly affect circadian timing and, in turn, a variety of other physiological functions. Little is known about the genes that regulate DCV biogenesis and cargo packaging. To study this problem we made a transgenic worm (C. elegans) expressing IA-2::GFP which was expressed in many neurons. We then mutagenized these worms with methanesulfonate. About one-half million worms were visually screened with a dissecting fluorescence microscope for high and low expression of IA-2::GFP in the neurons of mutagenized as compared to non-mutagenized worms. One of these worms (designated gv560) showed high expression of IA-2::GFP in many neurons and further studies revealed that the mutation occurred in the zinc finger transcriptional repressor pag-3. Electron microscopy revealed a marked increase in the number of DCV. To our knowledge, this is the first mutation identified that results in increased biogenesis of DCV. Screening of mutagenized worms expressing IA-2::GFP should lead to the discovery of other genes that regulate DCV biogenesis and cargo packaging.